The gimp-libgimp package contains libraries which are used to
communicate between the GIMP (GNU Image Manipulation Program) and
other programs which function as GIMP plug-ins.
If you are going to develop or use plug-ins for the GIMP, you'll need
to install the gimp-libgimp package. You'll also need to install the
gimp and gimp-devel. If you plan on using the GIMP, you'll probably
also want to install gimp-data-extras, which is not required but
contains a lot of extras which will be useful to GIMP users.